In Japan, ships are so familiar that we barely notice them. Tankers enter our ports, container vessels cross the horizon, and cargo moves through Yokohama, Kobe, Nagoya and countless smaller harbours every day. Only when a supply chain breaks, fuel prices rise or an international crisis threatens a shipping route do we remember how much of our lives arrives by sea.
That dependence is not a weakness. It is part of what made Japan what it is. For centuries, the sea has provided food, trade and contact with the wider world. Modern Japan built much of its prosperity through shipping, shipbuilding and the ability to transform imported resources into products valued around the globe.
The next question is what will power those ships in a world trying to reduce its dependence on fossil fuels.
Shipping is one of the most difficult parts of the energy transition. Large vessels travel enormous distances and must carry enough energy to complete their journeys. Batteries can work well for ferries, harbour vessels and some shorter routes, but a container ship crossing the Pacific presents a very different challenge. The weight of the batteries alone could take up space needed for cargo.
Hydrogen, ammonia and methanol are receiving serious attention. Each may have a role, but all must be produced, transported, stored and supplied at ports around the world. Producing them with low emissions will also require large amounts of clean electricity. The engineering is possible. Building the full international system will take time and money.
This is why the renewed interest in nuclear-powered shipping deserves a fair hearing.
In July 2026, the Port of Long Beach in California signed a nonbinding Memorandum of Cooperation with the United States Maritime Administration to examine possible uses of small modular reactors in ports, ships and other maritime infrastructure. No reactor has been approved, and neither side has committed to building one. Even so, the agreement matters because Long Beach is a major commercial port dealing with practical energy problems rather than an institution promoting nuclear technology.
Ports are electrifying cranes, cargo equipment and trucks. More ships are expected to switch off their engines while docked and use electricity supplied from shore, reducing air pollution for people who live nearby. These changes are welcome, but they also create large new demands for electricity at sites where land is scarce and work continues around the clock.
Wind and solar power can supply part of that electricity. Storage and improved grids will also help. A small reactor could offer something different: a compact source of low-carbon power that operates continuously. Every port would have to be assessed on its own conditions, but dismissing the idea before examining it would make little sense.
There is also movement on nuclear propulsion itself. In 2025, DNV granted Approval in Principle to a South Korean concept for a 15,000-container vessel powered by small modular reactors. This was an early engineering milestone, far from approval to construct or operate a commercial ship. It showed, however, that the concept had advanced beyond an attractive illustration and was ready for more detailed technical work.
The attraction of nuclear propulsion is clear. Nuclear fuel contains an extraordinary amount of energy in a small volume. In principle, a nuclear-powered cargo vessel could operate for years without the regular refuelling required by an oil-powered ship. It would also avoid carbon dioxide emissions from burning fuel during its voyages.
Navies have used nuclear propulsion for decades, but commercial shipping is a different world. Merchant ships move between countries, operate under tight cost pressures and may be owned, registered and crewed in several jurisdictions at once. A reactor that works well technically still has to fit into that complicated international system.
The regulatory questions are real. Who inspects the reactor when the ship enters a foreign port? Who carries liability if something goes wrong? Where can repairs be performed? What emergency arrangements should be in place for a collision, fire or grounding?
The International Maritime Organization adopted its current Code of Safety for Nuclear Merchant Ships in 1981. It is now working to update that framework for modern reactor technology. The current work plan envisages adoption of a revised code and related amendments around 2030, although the timing will depend on the progress of international negotiations.
Public confidence will matter just as much as regulation. People living near ports will want evidence that these ships can be operated safely. They will ask about security, used fuel and emergency response. Those questions are reasonable. Nuclear developers will have to answer them openly and early, rather than treating public concern as an obstacle to be managed later.
Nuclear power will not be suitable for every vessel. Ferries, fishing boats, tankers and container ships have different needs. The cleaner shipping system of the future will probably use several fuels and technologies. Nuclear may find its place first in the largest vessels, on specific routes, or as a source of electricity at major ports.
Japan should be closely involved in finding out.
Few countries have Japan’s combination of maritime experience, shipbuilding capability and nuclear engineering knowledge. Japan also understands that energy security depends on the ships, ports and sea routes that bring physical resources into the country.
Nuclear-powered commercial shipping may succeed, or it may prove too costly and complicated for widespread use. That is still an open question. What would be strange is for Japan, a country shaped by both the sea and advanced engineering, to leave the answer entirely to others.